Medical assay instrumentation requires the use of reagents and/or samples, such as blood samples in immunoassays, stored in a machine and added to a prepared sample. In typical medical assay instrumentation, a prepared sample is added to a cuvette or other vessel mounted on the machine. The particular reagent required for the given test is brought on station from a tray, or carousel, containing a number of different reagents. Whilst on station, the reagent container is opened, and a pipette inserted into the reagent in order to withdraw a volume of fluid. The pipette is then moved by the machine into a position directly above the cuvette and the required volume of reagent is typically dispensed into the cuvette by a positive displacement pump, for example, a syringe driven by a stepper motor. Following the dispensing of the reagent, the pipette is then moved off station, and the pipette tip is washed and rinsed, or alternatively discarded in the case of a disposable pipette. This dispensing process is complex and expensive, particularly where the pipette is washed and rinsed following each dispense of reagent. Furthermore, the machine is required to move the pipette from the reagent container to the cuvette and then to a further position at which the pipette is washed. This movement adds to the complexity of the machine, leading to an increased risk of component failure. Additionally, the movement of the machine leads to a long cycle time for each of the reagent dispenses. This in turn limits the throughput of the machine, and thereby the speed with which the laboratory can return the test results to the health care professionals.
A known solution to this problem is to provide a cartridge which contains both a reservoir of reagent and a multi-use dispense tube. This solution is advantageous in that the dispense tube does not need to be washed or discarded after each dispense. Also, the movement of the machine is limited to the delivery of the required cartridge to a dispense station. As soon as the delivery of reagent is completed, the next reagent cartridge can be brought into position.
In WO 2005/019092, a reagent dispensing cartridge includes a reagent reservoir, a reagent dispensing assembly in communication with the reagent reservoir and an actuator assembly. The reagent dispensing assembly includes a reagent metering chamber, a piston moving within the metering chamber, and two spring loaded one-way ball valves. The reagent reservoir includes a collapsible fluid bladder supported in a rigid cover. Piston displacement in one direction causes an amount of fluid to enter the metering chamber through the valve positioned between the fluid reservoir and the metering chamber, and piston displacement in the other direction propels the fluid out of the metering chamber. The dispensing cartridge is however complex to fabricate and is not disposable.
WO 2006/048643 discloses a dispensing system dispensing sub-milliliter volumes of reagent and comprising a cartridge, an armature and a nozzle assembly. The cartridge comprises a hollow body, which is divided into a first chamber and a second chamber by a valve seat. The first chamber forms a reservoir which, in use, retains reagent to be dispensed by the system. The second chamber defines an axial armature bore within which the armature can move. The nozzle assembly retains the armature in the bore. The reagent dispensing system also includes a solenoid coil of conventional construction having a bore. The second chamber of the cartridge is adapted to be mounted within the bore, thereby enabling the magnetic field generated by the coil to move the armature. Movement of the armature causes reagent from the reservoir to be expelled through the nozzle assembly. Here, the disposable parts including the cartridge, armature and nozzle assembly are rather complex and expensive to manufacture.
The reagent cartridge disclosed in patent number WO 2007/122387 comprises a reagent reservoir in fluid communication with a deformable dispense tube that is a least partially compressible to dispense a known volume of reagent from the tube. Compression of the tube is performed by a hammer actuated by a piezoelectric actuator. Despite its simplicity, the disposable cartridge is not convenient in use. Indeed, since the tube has a very small internal diameter, the volume of fluid dispensed by a single strike of the tube is in the order of 100 nanoliters. Dispensing larger volumes of reagent requires cycling the hammer, possibly slowing down the dispensing operation. Moreover, dispensing accurate volumes of reagent requires the carefully alignment of the tube with the hammer, an operation that must be performed for each cartridge and requires specific skills form the operator.